Field of the Invention
This invention relates generally to organic light emitting diodes, solar or photovoltaic (PV) cells, daylighting windows, and, more particularly, to a substrate having increased light scattering for improved light utilization.
Technical Considerations
An organic light emitting diode (OLED) is a light-emitting device having an emissive electroluminescent layer incorporating organic compounds. The organic compounds emit light in response to an electric current. Typically, an emissive layer of organic semiconductor material is situated between two electrodes (an anode and a cathode). When electric current is passed between the anode and the cathode, the organic material emits light, OLEDs are used in numerous applications, such as television screens, computer monitors, mobile phones, PDAs, watches, lighting, and various other electronic devices.
OLEDs provide numerous advantages over conventional inorganic devices, such as liquid crystal displays. For example, an OLED functions without the need for a back light. In low ambient light, such as a dark room, an OLED screen can achieve a higher contrast ratio than conventional liquid crystal displays. OLEDs are also thinner, lighter, and more flexible than liquid crystal displays and other lighting devices. OLEDs also require less energy to operate.
However, one disadvantage with OLED devices is that they typically emit less light per unit area than inorganic solid-state based point-light sources. In a typical OLED lighting device, about 80% of the light emitted from the organic material is trapped inside the device due to the optical waveguide effect in which the light emitted from the organic emitting layer is reflected back from the interface of the organic emitting layer/conductive layer (anode), the interface of the conductive layer (anode)/substrate, and the outer surface of the substrate. Only about 20% of the light emitted from the organic material escapes the optical waveguide effect and is emitted by the device. Therefore, it would be advantageous to provide a device and/or method to extract more light from an OLED device than is possible with conventional methods.
Photovoltaic solar cells are in principle counterparts to light emitting diodes. Here, the semiconductor device absorbs the energy of light (photons) and converts that energy into electricity. Similar to OLEDs, the efficiency of the photovoltaic device is relatively low. At the module level, for example, only up to 20% of the incident light is typically converted to electric energy. In one class of photovoltaic devices, those consisting of thin film PV cells, this efficiency can be as low as 6-7%, depending on the semiconducting material and the junction design. One way to increase the efficiency of the photovoltaic device is to increase the fraction of the solar light that is absorbed near the photovoltaic semiconductor junction. Thus, the present invention also finds use in the field of solar cells.